The present invention relates to a method and apparatus for recording keyboard music for re-creation on a similar keyboard instrument by actuation of the keys and, more particularly, to the detection, encoding, recording and reproduction of expression effects on electronic keyboard instruments. Expression control has been provided in a number of ways in the prior art. For example, transducers, such as microphones, accelerometers or magnetic pickups produce analog voltages which are proportional to the intensity with which the keys are struck. The analog information is then digitized in an analog to digital converter and combined with the keyboard switch actuation signals. These prior art systems do not take into account the delay between which the key switch is actuated and the actual production of the musical note involved nor do they take into account the mechanical differences between the production of notes in the treble range as compared to the production of notes in the bass range. The digital multiplex word format placed the expression bits for both bass expression and treble expression in one position in each frame.
According to this invention the key data from the key switch multiplexer is applied to a pair of serially connected 128-bit shift registers. The output of the first shift register is supplied to the second shift register and to an OR gate along with the output of the second shift register so that every key switch closure or actuation extends over two time frames and is, in effect, a note stretcher. This note stretching removes the very sharp and mechanical sound from short notes.
The key switch closures (data bits) are divided into two groups, bass and treble, in each time frame of data cells, the first group being assigned to a first group of data cells in the time frame and the second group or set of data cells being adapted to receive the second group of key switch closures (data bits). According to the invention the bass expression bits are inserted into data cells in each time frame in a position just in advance of the data cells containing the key switch closures of the group the expression data pertains to. Thus the bass expression bits are carried in data cells in the time frames preceding and contiguous to the bass note data cells and the treble note expression bits are carried in bit or data cell positions of the time frame just preceding the cells assigned to carry treble note data bits. This format or bit assignment assures a closer and more faithful rendition and reproduction of the original musical presentation.